1. Field of the Invention
The present invention relates to an auto-cruise controller to control the travel speed of a vehicle so that the actual speed is equal to the target speed.
2. Description of the Related art
Generally, in the auto-cruise controller of prior systems, the target speed of the vehicle is set corresponding to the speed of the vehicle when an auto-cruise switch is set as the vehicle travels and the throttle angle of an engine is calculated so that the detected actual vehicle speed is equal to the target vehicle speed, and the control is carried out with a predetermined control period so that a predetermined throttle angle can be obtained.
Then, when the vehicle comes to such a state that the target vehicle speed and the actual vehicle speed are almost balanced with each other with the fully closed throttle on a descending slope condition, fully closed and slightly opened conditions of the throttle repeatedly occur by the control of the auto-cruise, and as a result, the fuel-cut condition by the fully closed throttle and the return of the throttle to an opened condition are repeated, resulting in hunting of the fuel-cut.
Further, in the case where, while a switch is turned on in the deceleration direction during auto-cruising, the vehicle speed is decelerated at a predetermined deceleration, and when it is turned off, the target vehicle speed is downwardly adjusted; so-called coast adjustment is conducted, or in the case where the actual vehicle speed is converged into the target vehicle speed by a predetermined deceleration when the actual vehicle speed is increased some degree higher than the target vehicle speed by the temporary acceleration at the time of passing or the like, the constant deceleration control is carried out. In this case also, the fully closed condition and the slightly opened condition of the throttle are repeated in its constant deceleration control, resulting in hunting of the fuel-cut.
The problem to be solved is as follows: only by controlling the throttle angle of an engine so that the actual vehicle speed is equal to the target vehicle speed, a situation occurs in which the fully closed condition and the slightly opened condition of the throttle are repeated at the time of descending a slope or the constant deceleration control of the vehicle in the auto-cruising, and the hunting of the fuel-cut occurs.